Signal Transduction in Cells

Cells in our body are surrounded
by a lipid membrane. The "water-loving" heads of the
phospholipid molecules (blue) are directed towards the
outer and inner surfaces of the membrane. Many proteins
stretch through the entire membrane.
A first messenger (1), a molecule of adrenaline,
binds to a specific adrenaline receptor (2), a
discriminator. Thereby, the transducer (3), a G
protein - composed of alpha-, beta- and gamma subunits
- is activated.

This, in turn,
stimulates the amplifier (4), adenylate cyclase,
which produces (5) the second messenger, cyclic
AMP, from (6) ATP (adenosine-
triphosphate).(7) A cascade of enzymatic reactions alters the
behaviour of the cell and (8) via
phosphorylation (9) glycogen is transformed to
(10) glucose, which the cell uses to generate
ATP.
Phosphorylation can also alter membrane proteins, for
example, ion channels (11).